The present invention relates to a refrigerating compressor control circuit and, more particularly, to such a refrigerating compressor control circuit, which controls the output voltage value subject to the status of the load at the compressor motor.
During the operation of a refrigerator, two problems may be encountered. One problem is the affect of the pressure of cooling agent in starting the compressor motor. The other problem is the way of saving power during running of the compressor. The cooling agent is compressed to the condenser and then condensed from gas state to liquid state. The liquid state cooling agent is further delivered through an expansion valve to an evaporator to absorb heat. When heated, the cooling agent is turned to gas state again, and then compressed to the condenser by the compressor. This action is repeated again and again. During the circulation of the cooling agent between gas state and liquid state, a pressure is produced in the piping. A certain time after shutdown of the refrigerator, the pressure in the piping reduces. If the compressor motor shut down suddenly during its operation, the operator cannot immediately start the compressor motor again because the pressure in the piping increases the load of the compressor motor. When starting the compressor motor under a high pressure, a high starting current will be produced, causing damage to the compressor motor. In order to prevent this problem, the operator must wait for a certain length of time, and then start the compressor motor after the pressure in the piping has been reduced to a low level. However, the operator cannot accurately judge the accurate pressure dropping time. An alternate way to prevent this problem is the use of a heat sensitive overload protective switch in conjunction with a relay. The heat sensitive overload protective switch automatically cuts off power supply from the compressor motor upon an overload. The relay automatically starts the motor within a set time. The use of the heat sensitive overload protective switch greatly increases the cost of the machine. Further, the heat sensitive overload protective switch has the drawbacks of a contact switch. With respect to the operation of the compressor motor, the initial current value (starting current) is high. After started, the compressor motor runs with relatively smaller current, which is within the rated current range. When an induction motor runs not at the full load, it consumes much power than the actual requirement because a certain amount of power is wasted. The percentage of wasted amount of power becomes greater when the load is relatively reduced.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a refrigerator compressor control circuit, which starts the compressor motor a length of time delay after a sudden shutdown, preventing damage to the compressor motor due to high pressure of cooling agent. It is another object of the present invention to provide a refrigerator compressor control circuit, which controls the output voltage value subject to the status of the load at the compressor motor, so as to save power consumption. According to the present invention, the refrigerator compressor control circuit comprises a CPU (central processing unit), a current phase detector, a voltage phase detector, a trigger circuit having a TRIAC, a voltage level detector, a high current detector, a low current detector, an input filter, and an output filter. The current phase detector comprises a photo coupling crystal connected between the CPU and the TRIAC of the trigger circuit, and is adapted for detecting current phase and providing a feedback signal to the CPU to determine the triggering angle. The voltage phase detector is connected between the AC power supply and the CPU, comprised of a plurality of diodes and resistors, and adapted for detecting the time of zero voltage so as to obtain the voltage phase, for enabling the CPU to measure the load of the compressor motor by comparing the voltage phase obtained from the voltage phase detector with the current phase obtained from the current phase detector so as to determine the triggering angle of the TRIAC of the trigger circuit. The trigger circuit comprises a photo coupling crystal and the TRIAC, the TRIAC having a first end connected to AC power supply, a second end connected to the CPU through the photo coupling crystal of the trigger circuit, and a third end connected to the load of the compressor motor of the refrigerator. The voltage level detector is comprised of a diode, a capacitor, and a plurality of resistors, and adapted for detecting input voltage and providing the detected input voltage value to the CPU, causing the CPU to stop sending signal to the trigger circuit and to turn off the trigger circuit when the input voltage value surpasses a predetermined level. The high current detector is comprised of a plurality of resistors, a capacitor, and a grounded comparator, and adapted to provide a signal to the CPU immediately when the current at the load of the compressor motor of the refrigerator surpasses a predetermined high current level, causing the CPU to shut down the refrigerator. The low current detector is comprised of a plurality of resistors, a capacitor, and a grounded comparator, and adapted for providing a signal to the CPU immediately when the current at the load of the compressor motor of the refrigerator drops below a predetermined low current level, causing the CPU to make a full voltage output to start the compressor motor of the refrigerator at 0 triggering angle. The CPU has set therein predetermined control signal parameter values and start time value subject to the load of the compressor motor of the refrigerator, and adapted for receiving signals from the other sub-circuits of the refrigerating compressor control circuit, comparing the signals received, and outputting a control signal to the compressor motor of the refrigerator subject to the comparison result.